Insignia dpf

Hi got a 2011 insignia 2.0 dth and when I bought it it had fault come up on dash say dpf full and service vehicle soon took it to garage and they said they would do forced regen but after 2 mins it revved right up and diag said switch engine off, they started it again and done same thing again he said it was diesel runaway and it was smoking and only running on 3, he said it could be injector but he drained oil there was double amount in sump, I picked it up and drove home and the smoke cleared after 2 miles but still misfiring put another injector on but still missin